Because of its low noise and high energy efficiency, the hydraulic striking device is widely used for the jobs of destruction and crushing in construction, reconstruction or repairing of roads, buildings, etc. As known from the disclosure in, for example, the Japanese Examined Patent Application No. 52914/1985 (Kokoku) and U.S. Pat. No. 4,444,274, the hydraulic striking device comprises a slidable piston which is reciprocated under the hydraulic pressure to drive or hammer a tool such as chisel or the like.
The hydraulic striking device of such conventional type is operated as fed from a dedicated hydraulic pressure source or a so=called hydraulic unit. However, use of such a dedicated hydraulic unit will unavoidably cause the equipment cost, installation space, running cost, etc. to increase. To avoid such disadvantages, it has been proposed to operate the hydraulic striking device with a hydraulic pressure supplied from the hydraulic unit incorporated as standard component in a hydraulically driven machine, for example, hydraulic construction machine such as power shovel, bulldozer, wheeled loader, hydraulic crane truck or the like.
Since this system requires no dedicated hydraulic pressure source, the hydraulic striking device can be used in a wider industrial application. Also the hydraulic unit of a hydraulic construction machine can be effectively utilized as the power source of the device, and thus a civil engineering or construction work as a whole can be done more efficiently with such a hydraulic striking device.
However, the hydraulic construction machines vary in design very much from one to another, and accordingly the powers they supply also vary in pressure and flow rate significantly from one to another. On the other hand, as the flow rate of a hydraulic fluid supplied from the hydraulic pressure source to the hydraulic striking device varies, the operating pressure (pressure per unit area for driving the hammer piston) varies correspondingly. That is, a higher flow rate of the hydraulic fluid supplied from the hydraulic pressure source leads to an increased operating pressure, while a lower hydraulic fluid flow rate causes a decreased operating pressure.
Further, the impact given to a tool by the down-stroke piston of the hydraulic striking device is generally proportional to the operating pressure. Therefore, the operating pressure must be kept at a certain level when crushing a concrete or the like. Namely, if the operating pressure is too low, the impact given to the tool is also too low for the device to perform the function of striking. On the contrary, if the operating pressure is too high, the impact given to the tool becomes excessively large, causing the device parts to be heavily abraded or causing an excessively large vibration, which will make it difficult to handle the hydraulic striking device or eventually cause a great danger. That is, simple connection of the hydraulic pressure from the hydraulic pressure source of a hydraulic construction machine to the hydraulic striking device will not permit the device to work well and stably.
For a good and stable operation of the hydraulic striking device, it has been proposed to use the controller of the hydraulic pressure source or hydraulic unit of a hydraulic construction machine to limit the flow rate of the hydraulic fluid supplied to the hydraulic striking device to a certain range (for example, 20 to 25 liters/min). However, this method necessitates it to adjust the discharge rate at the hydraulic construction machine side each time when the hydraulic striking device is used with the machine. Such adjustment is very complicated and also takes much labor and time. Moreover, to use the construction machine for another job (its original function) after combined use with the hydraulic striking device, the controls and valves must be readjusted for the hydraulic pressure to match the working capacity of the construction machine. This is also troublesome. Neglecting of the discharge rate adjustment and inappropriate readjustment have frequently used to cause the failure of the hydraulic striking device.